QT prolongation: Difference between revisions
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==Background== | ==Background== | ||
[[File:SinusRhythmLabels.svg|thumb]] | |||
[[File:Grid.png|thumb]] | |||
*Prolonged ventricular repolarization → increased risk of ventricular arrhythmias | *Prolonged ventricular repolarization → increased risk of ventricular arrhythmias | ||
**Males >440-450 ms | **Males >440-450 ms | ||
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**Rate dependent and should become proportionately shorter with increasing heart rate | **Rate dependent and should become proportionately shorter with increasing heart rate | ||
=== | ===List of Drugs Causing QT Prolongation=== | ||
*[[Antiarrhythmics]] | *[[Antiarrhythmics]] | ||
**[[Amiodarone]], disopyramide, dofetilide, [[flecainide]], ibutilide, mexiletine, [[procainamide]], [[quinidine]], [[sotalol]] | **[[Amiodarone]], disopyramide, dofetilide, [[flecainide]], ibutilide, mexiletine, [[procainamide]], [[quinidine]], [[sotalol]] | ||
| Line 55: | Line 57: | ||
==Differential Diagnosis== | ==Differential Diagnosis== | ||
{{Syncope causes}} | |||
==Evaluation== | |||
===Workup=== | |||
*[[ECG]] | |||
*CBC | |||
*Chem 10 | |||
===Diagnosis=== | |||
[[File:De-Acquired longQT (CardioNetworks ECGpedia).jpg|thumb|Acquired QT prolongation]] | |||
*[[ECG]] | |||
**On visual inspection, QT takes up more than half the R-R distance | |||
**Measure QT interval in lead II or V5-6 | |||
**QTc = QT /√R-R | |||
===Determining Cause=== | |||
*Pause Dependent (Acquired) | *Pause Dependent (Acquired) | ||
**Drug induced | **Drug induced (see drug list above) | ||
***[[Antiarrhythmics]] | ***[[Antiarrhythmics]] | ||
***[[Phenothiazines]] | ***[[Phenothiazines]] | ||
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***[[CVA]] (subarachnoid) | ***[[CVA]] (subarachnoid) | ||
***Autonomic surgery (catechol excess: neck dissection, carotid endarterectomy, truncal vagotomy) | ***Autonomic surgery (catechol excess: neck dissection, carotid endarterectomy, truncal vagotomy) | ||
==Management== | ==Management== | ||
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*[[Hypomagnesemia]] | *[[Hypomagnesemia]] | ||
*[[Hypermagnesemia]] | *[[Hypermagnesemia]] | ||
== Calculators == | |||
{{QTc_Calculator}} | |||
==External Links== | ==External Links== | ||
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==References== | ==References== | ||
<references/> | <references/> | ||
[[Category:Cardiology]] | [[Category:Cardiology]] | ||
[[Category:Toxicology]] | [[Category:Toxicology]] | ||
Latest revision as of 15:07, 21 March 2026
Background
- Prolonged ventricular repolarization → increased risk of ventricular arrhythmias
- Males >440-450 ms
- Females >500 ms
- Rule of thumb: Normal QT interval is less than half of preceding RR interval
- QT interval is from the beginning of the Q wave to the end of the T wave
- Rate dependent and should become proportionately shorter with increasing heart rate
List of Drugs Causing QT Prolongation
- Antiarrhythmics
- Amiodarone, disopyramide, dofetilide, flecainide, ibutilide, mexiletine, procainamide, quinidine, sotalol
- Antibiotics
- Macrolide
- Fluoroquinolone
- Ciprofloxacin, gatifloxacin (most common), gemifloxacin, levofloxacin, moxifloxacin, ofloxacin
- Other
- Pentamidine, telithromycin, trimethoprim-sulfamethoxazole
- Antidepressants
- Amitriptyline, citalopram, doxepin, fluoxetine, nortriptyline, paroxetine, sertraline, venlafaxine
- Antiemetics
- Dolasetron, droperidol, granisetron, ondansetron
- Antifungals
- Antihypertensives
- Antineoplastics
- Lapatinib, nilotinib, sunitinib, tamoxifen
- Antimalarials
- Chloroquine, halofantrine
- Antipsychotics
- Chlorpromazine, clozapine, galantamine, haloperidol, lithium, paliperidone, pimozide, quetiapine, risperidone, thioridazine, ziprasidone
- Antivirals
- Amantadine, atazanavir, foscarnet
- Diuretics
- Indapamide
- Immune suppressants
- Opiates
- Phosphodiesterase inhibitors
- Skeletal muscle relaxants
- Urinary antispasmodics
- Solifenacin
Clinical Features
- Most are asymptomatic
- History may include:
- Syncope
- Cardiac arrest
- Family history of long QT or sudden death
- Medication history may include QT prolonging medications
Differential Diagnosis
Syncope Causes
- Cardiovascular-mediated syncope
- Dysrhythmias:
- Cardiovascular disease
- Neurally mediated syncope
- Vasovagal:
- Fear, pain, emotion, valsalva, breath-holding spell
- Situational (associated with):
- Vasovagal:
- Orthostatic hypotension-mediated syncope:
- Volume depletion:
- Autonomic Dysreflexia
- Autonomic failure due to meds
- Other serious causes
- Stroke
- SAH
- TIA
- Vertebrobasilar Insufficiency
- Subclavian steal
- Heat syncope
- Hypoglycemia
- Hyperventilation
- Asphyxiation
- Seizure
- Narcolepsy
- Psychogenic (anxiety, conversion disorder, somatic symptom disorder)
- Toxic (drugs, carbon monoxide, etc.)
Evaluation
Workup
- ECG
- CBC
- Chem 10
Diagnosis
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- ECG
- On visual inspection, QT takes up more than half the R-R distance
- Measure QT interval in lead II or V5-6
- QTc = QT /√R-R
Determining Cause
- Pause Dependent (Acquired)
- Drug induced (see drug list above)
- Electrolyte Abnormalities (hypoKalemia, hypoMag, hypoCa)
- Hypokalemia triad
- Long QT, ST depressions, PVCs
- Hypokalemia triad
- Hypothermia
- Diet related (starvation, low protein)
- Severe Bradycardia/AV Block
- Hypothyroid
- Contrast injection
- CVA (intraparenchymal)
- Elevated intracranial pressure and Intracranial hemorrhage
- MI
- Adrenergic Dependent
- Congenital
- Jarvel/Lange-Nielsen
- (+deafness; AR)
- Romano-Ward syndrome
- (normal hearing; AD)
- Sporadic
- Mitral valve prolapse
- Jarvel/Lange-Nielsen
- Acquired
- CVA (subarachnoid)
- Autonomic surgery (catechol excess: neck dissection, carotid endarterectomy, truncal vagotomy)
- Congenital
Management
Pause Dependent (precipitated by bradycardia)
- Unstable/sustained torsades→ defibrilation (unsynchronized)
- Stable
- Treat underlying etiology
- Increase HR >80 (isoproterenol or overdrive pacing)
- Magnesium sulfate IV
- Consider lidocaine, transvenous pacing[1]
Adrenergic Dependent (precipited by tachycardia)
- Unstable/sustained torsades→ defibrilation (unsynchronized)
- Stable
- Slow HR (beta-blockers)
- May consider magnesium sulfate
Disposition
- Consider admission, especially for QT >500 or if symptomatic
- May require consultation for discontinuation of QT prolonging medications
- Avoid prescribing medications that may contribute to prolonged QT
See Also
Calculators
Corrected QT Interval (QTc)
| Parameter | Value |
|---|---|
| QT Interval (ms) | |
| Heart Rate (bpm) | |
| RR Interval (ms) — auto-calculated from HR | ms |
| Results | |
| QTc (Bazett's) — QT / √(RR in sec) | ms |
| QTc (Fridericia) — QT / ∛(RR in sec) | ms |
| Interpretation (Bazett's QTc) | |
|---|---|
| <440 ms | Normal QTc for males. |
| <460 ms | Normal QTc for females. |
| 440–500 ms | Borderline/Prolonged — Monitor closely. Review medications for QT-prolonging drugs. |
| >500 ms | Significantly prolonged — High risk for Torsades de Pointes. Discontinue offending agents. Check Mg²⁺/K⁺/Ca²⁺. |
| References |
|---|
|
External Links
References
- ↑ Simon HL, Behr ER. Pharmacological treatment of acquired QT prolongation and torsades de pointes. Br J Clin Pharmacol. 2016 Mar; 81(3): 420–427. doi: 10.1111/bcp.12726